High-mineral oyster extract and a process for manufacturing the same

ABSTRACT

The present invention provides a process for extracting minerals from mineral-rich oysters and furthermore provides an oyster extract containing the minerals, and taurine, glycogen, and nucleotides. First, raw oysters are subjected to hot water extraction to obtain soluble ingredients and to remove unwanted components, and then the residue is extracted with acid solution of pH 2 to 4.. The extract is neutralized with alkali to obtain a precipitate having a high content of minerals such as zinc. The oyster extract obtained by this process contains zinc in the amount of 6% to 13% by dry weight.

FIELD OF THE INVENTION

[0001] The present invention relates to an oyster extract containinglarge amounts of minerals such as zinc and manganese, and also relatesto a process for manufacturing the same.

BACKGROUND OF THE INVENTION

[0002] Recently, minerals have become recognized as important elementsfor human health. For example, a deficiency of zinc or manganese causestaste abnormality or growth disorder of the human body. This deficiencyis caused by a change in the kinds of food eaten or in eating habits. Itis very important to take these minerals every day for preventingdiseases.

[0003] The oyster, or Crassostrea gigas is well known as a perfectnutritious food, because it contains large amounts of nutritiouscomponents compared with other foods. However, it is not advisable totake oysters as daily food, because they tend to cause allergy andbecause of the accumulation of heavy metals contained in oysters. Inaddition, the ingredients of the oysters change depending on the seasonor place from which they were harvested.

[0004] To solve these problems, oyster extract tablets have beendeveloped and marketed as a healthy food, which tablets are generallyprepared by extracting oysters with water or hot water as disclosed inJapanese Patent Publication Kokoku Hei 4-63672(1992-63672 B2). In thismethod, an oyster extract is obtained by hot water extraction at 50 to90° C. for 2 to 3 hours, and ethanol is then added to the extract toobtain a precipitate.

[0005] Although water soluble ingredients such as taurine, glycogen, andother substances are extracted with water, water-insoluble minerals suchas zinc, manganese, and other minerals can not be extracted by water orhot water. Therefore, large amounts of minerals remain in the residue ofthe oyster extracted by these means.

DESCRIPTION OF THE INVENTION

[0006] One objective of the present invention is to provide an oysterextract rich in minerals, which thus requires an effective extractionprocess for water-insoluble minerals such as zinc and manganese from theoyster extract residue.

[0007] Another objective of this invention is to provide an oysterextract containing the conventional components of the oyster extract,such as taurine, glycogen, and nucleotides, and the minerals mentionedabove.

[0008] The present invention is based on the finding thatwater-insoluble ingredients contained in oyster, such as zinc,manganese, and other minerals, can be extracted under acidic conditions,more particularly by adding acid to the oyster residue after hot waterextraction.

[0009] A nutritious oyster extract is obtained by mixing the oysterwater-soluble extract containing taurine, glycogen, and nucleotides asmain ingredients disclosed in prior arts with water-insoluble extractcontaining minerals such as zinc, manganese, and other minerals preparedby the method mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 shows a gel filtration chromatography pattern and zincconcentration in each fraction, obtained from a high-mineral oysterextract of the present invention.

[0011]FIG. 2 shows the UV absorption spectrum of a fraction ranging from3000 to 5000 daltons in molecular weight, which was separated from thehigh-mineral oyster extract of the present invention.

EMBODIMENTS OF THE INVENTION

[0012] Oysters are first extracted with hot water, and then the oysterresidue is extracted with an acid solution of pH from 2 to 4.Thereafter, the pH of the extract is brought to neutral to obtain aprecipitate of the oyster extract.

[0013] As disclosed in Japanese Patent Publication Kokoku Hei4-63672(1992-63672 B2), an oyster extract is obtained by hot waterextraction at 50 to 90° C. for 2 to 3 hours, and ethanol is added to theextract to obtain a precipitate. The precipitate is condensed to 20% to45% by dry weight. The extract contains taurine, glycogen andnucleotides.

[0014] Then the oyster residue from the hot water extraction issubjected to acid extraction.

[0015] If the oysters are extracted directly with acid solution, theproteins of the oyster are hydrolyzed at the high temperature, and theheavy metals contained in the internal organs of the oysters,chlorophyll-related substances, and unwanted proteins become a part ofthe extract.

[0016] Further, the useful ingredients are diluted and noxiousingredients are extracted by the direct acid extraction. In addition,the main ingredients disclosed in prior arts such as glycogen andnucleotide materials are denatured by the acid. Therefore, it isessential to employ the hot water extraction, which is effective toobtain water-soluble substances from oysters, prior to the acidextraction

[0017] Any acid is applicable to the present invention, for instance,hydrochloric acid, sulfuric acid or phosphoric acid as inorganic acids,and citric acid or acetic acid, as organic acids. It is not necessary tospecify the concentration and the volume of the acid solution

[0018] The pH of the oyster residue is adjusted to 1 to 4, or 2 to 3preferably, after adding the acid solution to the oyster residue, and ifthe pH exceeds 4, the extraction efficiency of minerals is reduced,because the raw oysters spontaneously buffer the change of pH, bringingthe pH of the solution to neutral.

[0019] The minimum extraction time is at least 1 hour, preferably 24hours. The temperature for the extraction is not specified, but roomtemperature is preferable. If the temperature is low, the extractionefficiency is decreased. On the contrary, if the temperature is high,the oysters are degraded and unwanted substances are extracted.

[0020] After the acid extraction, a solid-liquid separation procedure isconducted, for instance, filtration or centrifugation. The solidcomponent, which is separated from the extract, is about 2% to 5% of theextract.

[0021] The extract is neutralized by adding alkali, and a precipitate isobtained. The precipate is then centrifuged, and washed with water toremove the unwanted salts. The solid component, having a high content ofminerals is obtained after drying.

[0022] Preferable alkalis for neutralization are NaOH and KOH.

[0023] The oyster extract contains a large amount of zinc, 6% to 14% bydry weight. The preferable zinc range is 10% to 14% , or 12% to 14% bydry weight.

[0024] According to the analysis by gel filtration chromatography of theacid extract from raw oysters, zinc is found in high concentration inthe fractions of 3000 to 5000 daltons as molecular weight and in thoseover 8000. Therefore, zinc might be combined with various organicsubstances of raw oysters.

[0025]FIG. 1 shows the relation between the gel filtrationchromatography pattern of the high-mineral oyster extract of the presentinvention and the zinc concentration in each fraction.

[0026] As shown in FIG. 1, the largest amount of zinc is eluted in thefraction of 3000 to 5000 daltons as molecular weight (fractions nos. 39to 49 in FIG. 1).

[0027]FIG. 2 shows the UV absorption spectrum of the fraction of 3000 to5000 daltons as molecular weight, separated from the high-mineral oysterextract of the present invention.

[0028] As shown in FIG. 2, the absorption peaks in the UV spectrum areobserved at 257 nm and 219 nm.

[0029] In the high-mineral oyster extract of this invention, zinc ispossibly combined with a peptide of 3000 to 5000 daltons in the ratio of1:1.

[0030] Besides the zinc, magnesium, calcium and manganese are alsocontained in the high-mineral oyster extract of the present invention.Among these minerals, calcium and manganese, like zinc, might also becombined with the water-insoluble protein.

[0031] The extract obtained by this method contains highly concentratedminerals, zinc is 4 to 6 times as much, and manganese, calcium, andmagnesium are 2 to 3 times as much, by dry weight as contained in theraw oyster. The oyster extract according to this invention containsmanganese in the amount of 0.05% to 0.2% by dry weight.

[0032] The high-mineral oyster extract of the present invention may bemixed with the conventional oyster extract, such as the extract obtainedby the hot water extraction.

[0033] The mixture of these two extracts is a highly balanced nutritiousoyster extract containing minerals such as zinc and other nutritiouscomponents, such as taurine, glycogen, and nucleotides.

[0034] The mixture ratio of the high-mineral oyster extract and theconventional oyster extract is selectively determined depending on thedesired mineral level. For example, it is preferable to mix the two at aratio of 1 to 40(high-mineral/conventional).

[0035] The preferable zinc level in the oyster extract mixture is 0.05%to 0.4%, more preferably 0.2% to 0.4% or much more preferably 0.3% to0.4% by dry weight. The preferable taurine level is 3% to 7%, morepreferably 4% to 7% preferably, or much more preferably 5% to 7% by dryweight.

[0036] The mixture contains glycogen in amount of 30% to 60%, or 40% to60% preferably, or 50% to 60% by dry weight more preferably. Thepreferable manganese level is 0.002% to 0.005%, more preferably 0.003%to 0.005% or much more preferably 0.004% to 0.005% by dry weight. Thepreferable magnesium level is 0.4% to 1.2%, more preferably 0.5% to1.2%, or much more preferably 0.6% to 1.2% by dry weight.

[0037] The invention is explained in more detail with the followingembodiments of this invention, however, the present invention is notrestricted to the embodiments.

EXAMPLE 1

[0038] The raw oyster of 37.5g by dry weight is extracted with 65 g ofhot water of 80° C. for 3 hours. Thereby 8.4 g of oyster extract by dryweight is obtained.

[0039] For obtaining a high-mineral oyster extract, 0.1N—HCl is added tothe oyster residue which is kept at a room temperature. After 24 hours,the extract is filtered and neutralized by adding NaOH to obtain aprecipitate. The precipitate is centrifuged for removing water from theextract and washed with water to remove the unwanted salts. Theprecipitate is then heated to obtain the dried oyster extract.

[0040] Finally, 0.2 g by dry weight of oyster extract, which contains ahigh content of minerals, is obtained.

[0041] The compositions of each extract are shown in Table 1. TABLE 1Ash Yield Zn Mn Mg Ca Taurine Glycogen (%) (g) (ppm) (ppm) (ppm) (ppm)(Wt. %) (Wt. %) Raw oyster 20.3 37.5 2,568 84 5,717 1,453 3.50 33.0Residue 7.6 20.7 3,565 58 2,639 697 3.47 0.6 (hot water extraction)Extract (A) 35.6 8.4 582 32 8,171 590 4.05 43.5 High-mineral 41.9 0.2133,223 1,012 11,619 4,102 0.04 0.4 Extract (B) Mixture (A) + (B) 3,69255 8,249 3.96 42.5 (42:1)

[0042] As indicated in Table 1, the extract contains 5 times as muchzinc as raw oysters, 12 times as much manganese, 2 to 3 times as muchmagnesium and calcium. The nutritious oyster extract mixture is obtainedby mixing the hot water extract and the acid extract at a mixture ratioof 42 to 1, as shown in Table 1.

[0043] By our invention, it now becomes possible to obtain an oysterextract containing large amounts of minerals such as zinc and manganese.Furthermore an oyster extract that contains both the minerals such aszinc or manganese and water-soluble components such as taurine,glycogen, and nucleotides is obtained.

What is claimed:
 1. An oyster extract containing 6% to 14% zinc by dryweight, which mineral is combined with peptides of the oyster.
 2. Theoyster extract according to claim 1 , wherein the peptides havemolecular weight of 3000 to 5000 daltons as judged by the results of gelfiltration chromatography.
 3. The oyster extract according to claim 1 or2 , wherein the oyster extract is obtained by extracting oysters withhot water, adjusting the oyster residue to pH 2 to 4, and neutralizingthe residue to obtain a precipitate from the oyster extract.
 4. Theoyster extract according to one of claims 1, 2 or 3 wherein furthercontaining 0.05% to 0.2% of manganese by dry weight and 1% to 2% ofmagnesium by dry weight.
 5. An oyster extract mixture comprising theoyster extract according to any one of claims 1, 2, 3 or 4 and an oysterextract obtained by hot water extraction.
 6. An oyster extract mixturecontaining 0.05% to 0.4% zinc by dry weight, which mineral is combinedwith peptides of the oyster.
 7. The oyster extract mixture according toclaim 6 , wherein the extract further containing 3% to 7% taurine by dryweight and 30% to 60% glycogen by dry weight.
 8. The oyster extractmixture according to claim 6 , wherein the extract further containing 3%to 7% taurine by dry weight, 30% to 60% glycogen by dry weight, 0.002%to 0.005% manganese by dry weight, and 0.4% to 1.2% magnesium by dryweight.
 9. A process for manufacturing an oyster extract comprising thesteps of extracting oyster with hot water, then adjusting the oysterresidue to pH 2 to 4, filtering the residue extract and neutralizing thepH of the filtered extract to obtain a high-mineral precipitate of theoyster extract.